Polycarbonate resin, optical information recording medium substrate comprising the same, and optical information recording medium

ABSTRACT

A polycarbonate resin having an improved hue is provided, which is suitable for use as a substrate for transfer type optical recording media such as optical disks. 
     The polycarbonate resin is one obtained by reacting starting materials comprising a dihydric phenol, a carbonate material, and a chain terminator comprising a p-(long chain)-substituted phenol (hereinafter referred to as a para isomer), characterized in that the amount of an o-(long chain)-substituted phenol (hereinafter referred to as an ortho isomer) contained as an impurity in the chain terminator used satisfies the following relationship:                    (     ortho                 isomer                 amount     )         (     para                 isomer                 amount     )     +     (     ortho                 isomer                 amount     )         ×     10   6       ≤     10     (       0.31   ×     (     number                 of                   C   &#39;        s     )       +   0.8     )               (   i   )                         
     (wherein “number of C&#39;s” represents the number of carbon atoms in the substituent organic group of the substituted phenols).

This application is a Continuation-in-part (CIP) of U.S. applicationSer. No. 09/381,278, filed on Sep. 20, 1999, pending, which wasoriginally filed as International Application Number PCT/JP99/00113,filed Jan. 14, 1999.

TECHNICAL FIELD

The present invention relates to a polycarbonate resin, moreparticularly, a polycarbonate resin suitable for use as a substrate fortransfer type optical information recording media such as optical disks.The present invention further relates to a substrate for opticalinformation recording media which is formed from the polycarbonate resinand to an optical information recording medium employing the substrate.

BACKGROUND ART

Compared to conventional magnetic recording, optical recording, which iscapable of noncontact recording and reproducing, is characterized bybeing less influenced by marring or fouling and is contributing greatlyto an increase in storage capacity.

Recording media for use in this technique are constituted by forming aninformation recording layer on a transparent substrate made of, e.g., apolycarbonate resin. Polycarbonate resins are suitable for use as thematerial of substrates for the information recording media because theyhave satisfactory heat resistance in melt molding, reduced dimensionalchanges after molding, and excellent mechanical properties. In recentyears, with the increasing storage capacity in this field wherepolycarbonate resins are used, the distance between pit trackstransferred to a transparent substrate is becoming shorter and the depthof the pits are becoming larger. As a result, it has become usual tomold polycarbonate resins at higher molding temperatures and higher moldtemperatures. However, because of the insufficient heat resistance ofthe resins, molding at higher temperatures tends to yield low-molecularvolatiles, which deposit on the stamper and replicas to cause biterrors, leading to serious problems. The higher-temperature moldingfurther causes scorching due to resin deterioration, resulting in anincreased error frequency in the final products. Because of such variousproblems, there has been a desire for a material which can be molded ata lower temperature. On the other hand, the mold temperature also isbecoming higher so as to cope with the shorter distance between bittracks and the larger depth of pits. However, as the mold temperatureincreases, the problem of warpage of molded substrates becomes severer.There has hence been a desire for a lower mold temperature as in thecase of molding temperature.

Under these circumstances, polycarbonate resins have been stronglyrequired to be a material which can be molded at a lower moldingtemperature and a lower mold temperature without impairing importantproperties possessed by disk substrates (birefringence, suitability fortransfer, and warpage).

It has been well known in this respect that a polycarbonate resin whichitself has improved flowability is obtained by using an alkylphenol inwhich the alkyl chain is longer than in the alkylphenols conventionallyused as chain terminators for polycarbonate resins. For example, BritishPatent 965,457 discloses a technique of lowering melt viscosity by usinga long-chain monohydric alcohol as a chain terminator, while U.S. Pat.No. 3,240,756 discloses the use of an alkylphenol as a terminator. InUnexamined Published Japanese Patent Application No. 51-34992 are givenexamples in which a phenol, acid chloride, acid, or alcohol having analkyl group having 8 to 20 carbon atoms is used as a chain terminator toproduce a polycarbonate having improved flowability. Recently, examplesin which a polycarbonate resin having a long-chain alkyl group at eachterminal is used as an optical molded article are given in UnexaminedPublished Japanese Patent Application No. 60-203632 The above referenceseach states that an improvement in flowability is possible due to thelong-chain alkyl groups present at molecular ends of the polycarbonate.

However, it has been found that such a polycarbonate obtained with along-chain alkylphenol gives products having a far more yellowish hue ascompared with those obtained from the polycarbonates produced witht-butylphenol, which has been conventionally employed, and that thepolycarbonate is colored to such a degree that the molded products areunsuitable for use in optical recording media.

DISCLOSURE OF THE INVENTION

The present inventors have made intensive studies in order to eliminatethe problems of the prior art techniques described above. As a result,the present invention has been achieved.

One essential aspect of the present invention resides in a polycarbonateresin obtained by reacting starting materials comprising a dihydricphenol, a carbonate material, and a chain terminator comprising ap-substituted phenol (hereinafter referred to as a para isomer)represented by the following general formula (I), characterized in thatthe amount of an o-substituted phenol (hereinafter referred to as anortho isomer) contained as an impurity in the chain terminator usedsatisfies the following relationship (i):

(wherein R is an organic group having 6 to 30 carbon atoms)$\begin{matrix}{{\frac{\left( {{ortho}\quad {isomer}\quad {amount}} \right)}{\left( {{para}\quad {isomer}\quad {amount}} \right) + \left( {{ortho}\quad {isomer}\quad {amount}} \right)} \times 10^{6}} \leq 10^{({{0.31 \times {({{number}\quad {of}\quad {C'}s})}} + 0.8})}} & (i)\end{matrix}$

(wherein “number of C's” represents the number of carbon atoms in thesubstituent organic group of the substituted phenols).

Another essential aspect of the present invention resides in apolycarbonate resin obtained by reacting starting materials comprising adihydric phenol, a carbonate material, and a chain terminator comprisinga p-substituted phenol represented by the following general formula (I),characterized in that the polycarbonate resin, when molded at 360° C.and a cycle time of 180 seconds, gives molded objects (3.2 mm thick)having a YI of 2.5 or lower and a difference in YI between the firstshot and the tenth shot (hereinafter referred to as ΔYI) of 0.8 orsmaller:

(wherein R is an organic group having 6 to 30 carbon atoms).

Still another essential aspect of the present invention resides in asubstrate for optical information recording media which comprises thepolycarbonate resin, and in an optical information recording mediumemploying the substrate.

BEST MODES FOR CARRYING OUT THE INVENTION

The polycarbonate resin of the present invention is produced by reactingstarting materials comprising a dihydric phenol, a carbonate material,and a specific chain terminator.

The dihydric phenol used in the present invention is a compound havingtwo phenolic hydroxyl groups. This phenol is preferably a compoundrepresented by the general formula HO-Z-OH, wherein Z is an organicgroup comprising one or more aromatic nuclei, and one or more of thehydrogen atoms bonded to the carbon atoms of the aromatic nuclei eachmay be replaced with a chlorine atom, bromine atom, aliphatic group, oralicyclic group. The aromatic nuclei may differ from each other insubstituent. The aromatic nuclei may be bonded to each other with acrosslinking member. Examples of this crosslinking member includealiphatic groups, alicyclic groups, heteroatoms, and combinations ofthese.

Specific examples of the dihydric phenol include hydroquinone,resorcinol, dihydroxydiphenyl, bis(hydroxyphenyl)alkanes,bis(hydroxyphenyl)cycloalkanes, bis(hydroxyphenyl)sulfides,bis(hydroxyphenyl) ethers, bis(hydroxyphenyl)ketones, bis(hydroxyphenyl)sulfones, bis(hydroxyphenyl)sulfoxides,bis(hydroxyphenyl)di-alkylbenzenes, and derivatives thereof in which oneor more of the aromatic nuclei have one or more alkyl or halogensubstituents. Two or more of these dihydric phenols can be used incombination.

These dihydric phenols and other appropriate dihydric phenols are givenin, e.g., U.S. Pat. Nos. 4,982,014, 3,028,365, 2,999,835, 3,148,172,3,275,601, 2,991,273, 3,271,367, 3,062,781, 2,970,131, and 2,999,846,German Offenlegungschrifts 1,570,703, 2,063,050, 2,063,052,and2,211,956, and French Patent 1,561,518.

Preferred dihydric phenols include bisphenol s containing two phenolresidues in the skeleton, such as 2,2-bis(4-hydroxyphenyl)propane,2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane,1,1-bis(4-hydroxyphenyl)cyclohexane, and1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.

The carbonate material used in the present invention is a compoundcapable of forming carbonate bonds

in a polycarbonate main chain through a polymer -forming reaction, e.g.,a condensation reaction or exchange reaction. Examples thereof includephosgene and diphenyl carbonate.

Although processes for producing the polycarbonate resin in the presentinvention are not particularly limited, the interfacial polycondensationmethod using phosgene as a starting material is generally used. Therealso is a method in which phosgene is reacted with an alkylphenol tofirst produce a dialkyiphenyl carbonate and this carbonate is reactedwith a dihydric phenol under melt condensation conditions. However, thismethod, in which the molecular weight is increased bytransesterification under the conditions of a melting temperature (up to300° C.) and a high vacuum (≦50 mmHg) while distilling the alkyiphenol,is not always an industrially advantageous method because thedistillation becomes difficult as the length of the alkyl chain in thealkylphenol becomes longer.

The chain terminator used in the present invention is a substitutedphenol which has an organic group having 6 to 30 carbon atoms in thepara position and is represented by the following general formula (I):

(wherein R is an organic group having 6 to 30 carbon atoms).

Examples of the organic group R include alkyl groups, aryl groups,alkenyl groups, alkoxyl groups, and alkoxyalkyl groups, and thesesubstituents may be partly substituted with other atoms (O, S, N, etc.).The wide range of the number of carbon atoms is attributable mainly toprocesses for producing long-chain alkylphenols. In a generallyfrequently used reaction, phenol is caused to add the dimer of propyleneor isobutene or the trimer or tetramer of propylene with the aid of anacid catalyst. However, in the case of the reaction of propylenetetramer, for example, the propylene tetramer material generally usedhas a molecular weight distribution comprising the tetramer as the maincomponent and further containing smaller-molecular components andlarger-molecular components. It is therefore impossible to limit thenumber of carbon atoms although the main component can be specified.

Preferred of the above phenol compounds are p-alkylphenols representedby the following general formula (II):

(wherein R′ is an alkyl group having 6 to 30 carbon atoms).

Specifically, alkylphenols such as t-octylphenol, octylphenol,nonylphenol, dodecylphenol, and 3-pentadecylphenol are preferred.

If the number of carbon atoms in the alkyl group is too small, thephenol compound is ineffective in improving flowability during meltmolding and also in improving suitability for transfer in disk molding,although the impurity content is low and the product obtained has asatisfactory YI. If the number of carbon atoms therein is too large, theproduct obtained has an exceedingly reduced Tg, which is undesirable inthat this may result in disk warpage depending on molding conditions.Consequently, the number of carbon atoms is from 6 to 30, preferablyfrom 8 to 24, more preferably from 8 to 15, still preferably from 9 to15, still more preferably from 11 to 15, especially 12.

The present inventors have found that a chain terminator comprising sucha p-substituted phenol (hereinafter referred to as a para isomer)contains an o-substituted phenol (hereinafter referred to as an orthoisomer), which differs from the para isomer in the position of theorganic group substituent, as an impurity attributable to the processwhich has been used for producing the para isomer, and that byregulating the content of this ortho isomer, the hue of a polycarbonateresin product can be effectively improved. Namely, the hue of apolycarbonate resin is effectively improved by regulating a substitutedphenol comprising the para isomer and the ortho isomer so that theproportion of the ortho isomer is not larger than a specific value.

Specifically, the amount of the ortho isomer contained preferablysatisfies the following relationship (i): $\begin{matrix}{{\frac{\left( {{ortho}\quad {isomer}\quad {amount}} \right)}{\left( {{para}\quad {isomer}\quad {amount}} \right) + \left( {{ortho}\quad {isomer}\quad {amount}} \right)} \times 10^{6}} \leq 10^{({{0.31 \times {({{number}\quad {of}\quad {C'}s})}} + 0.8})}} & (i)\end{matrix}$

(wherein “number of C's” represents the number of carbon atoms in thesubstituent organic group of the substituted phenols).

More preferably, the amount thereof satisfies the following relationship(ii): $\begin{matrix}{\frac{\text{(ortho isomer amount)}}{\text{(para isomer amount)} + \text{(ortho isomer amount)}} \times {{10^{6} \leq 0^{({{0.31^{x}{({{number}\quad {of}\quad {C'}s})}} + 0.6})}}}} & ({ii})\end{matrix}$

(wherein “number of C's” represents the number of carbon atoms in thesubstituent organic group of the substituted phenols). Even morepreferably, the amount thereof satisfies the following relationship(iii): $\begin{matrix}{\frac{\text{(ortho isomer amount)}}{\text{(para isomer amount)} + \text{(ortho isomer amount)}} \times {{10^{6} \leq 10^{({{0.31^{x}{({{number}\quad {of}\quad {C'}s})}} + 0.5})}}}} & ({iii})\end{matrix}$

(wherein “number of C's” represents the number of carbon atoms in thesubstituent organic group of the substituted phenols) In each of theabove relationships (i) to (iii), the left side indicates theproportion, in terms of ppm, of the ortho isomer in the substitutedphenol. Hereinafter, this proportion is referred to as ortho isomercontent.

If the ortho isomer content is too high, the polycarbonate resin productobtained has a considerably impaired hue. On the other hand, regulatingthe ortho isomer content to an exceedingly small value is undesirablefrom the standpoint of producing a substituted phenol, e.g., analkylphenol, because the result is an impaired yield. By selecting anyof the above relationships (i) to (iii) according to purposes, anexcessive regulation can be avoided.

The chain terminator is preferably a p-substituted phenol which isrepresented by general formula (I) wherein R is an organic group having11 to 15 carbon atoms, more preferably a p-alkylphenol which isrepresented by general formula (II) wherein R′ is an alkyl group having11 to 15 carbon atoms, and in which the amount of an ortho isomercontained therein satisfies the following relationship (iv).$\begin{matrix}{{\frac{\text{(ortho isomer amount)}}{\text{(para isomer amount)} + \text{(ortho isomer amount)}} \times 10^{6}} < {10,000}} & ({iv})\end{matrix}$

This is because use of this chain terminator is effective in yieldingpolycarbonate resin products having not only an improved hue butimproved long-term reliability, which is an essential requirement indisk applications.

In relationship (iv), the ortho isomer content is preferably lower than9,500 ppm, more preferably lower than 9,000 ppm.

If the ortho isomer content is too high, the polycarbonate resin productobtained has a considerably impaired hue. On the other hand, regulatingthe ortho isomer content to an exceedingly small value is undesirablefrom the standpoint of producing a substituted phenol, e.g., analkylphenol, because the result is an impaired yield. Consequently, theortho isomer content, represented by the left side of relationship (iv),is generally 10 ppm or higher, preferably 100 ppm or higher, morepreferably 1,000 ppm or higher, whereby an excessive regulation can beavoided.

From the standpoint of producing a substituted phenol, e.g., analkylphenol, a means generally effective in reducing the ortho isomercontent therein may be fractionation by distillation. However, thisfractionation is not an easy means because the para and ortho isomersbasically have the same molecular weight. It is after all preferred toinhibit the ortho isomer from generating in the stage of reaction. Forexample, a satisfactory means for reducing the ortho isomer content isto prolong the reaction in an alkylation step conducted with the aid ofan acid catalyst or to prolong an isomerization reaction (orthoisomer→para isomer).

The use amount of a chain terminator in producing a polycarbonate resinvaries depending on the molecular weight of the target polycarbonateresin. However, in the case of the interfacial polycondensation method,for example, the amount thereof suitable for disk use is generally aboutfrom 1 to 9% by mole, preferably about from 4 to 8% by mole, morepreferably about from 5 to 7% by mole, based on the amount of thedihydric phenol in the aqueous phase.

On the other hand, the time when a chain terminator is added is notparticularly limited. However, if a chain terminator is added, forexample, in the presence of phosgene, condensates of the chainterminator itself (diphenyl carbonate, etc.) generate in a large amount,undesirably resulting in the accumulation of a large amount of reactionproducts which are apt to volatilize at higher temperatures. On theother hand, if the addition of a chain terminator is delayedexcessively, this is undesirable because molecular-weight control isdifficult. It can be said in conclusion that the addition of a chainterminator is preferably conducted during the period from immediatelyafter the termination of phosgene consumption to before the initiationof molecular-weight increase.

Any desired branching agent can be added in producing the polycarbonateresin. The branching agent to be used can be selected from variouscompounds having three or more functional groups. Appropriate examplesof the branching agent include 2,4-bis(4-hydroxyphenylisopropyl)phenol,2,6-bis(2′-hydroxy-5′-methylbenzyl)-4-methylphenol,2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)propane, and1,4-bis(4,4′-dihydroxytriphenylmethyl)benzene, which are compounds eachhaving three or more phenolic hydroxyl groups. Also included are2,4-dihydroxybenzoic acid, trimesic acid, cyanuric chloride,bis(4-hydroxyphenyl)-2-oxo-2,3-dihydroxyindole, and3,3-bis(4-hydroxy-3-methylphenyl)-2-oxo-2,3-dihydroindole, which arecompounds each having three functional groups. Preferred of these arethe compounds having three or more phenolic hydroxyl groups. Althoughthe use amount of the branching agent varies depending on the desireddegree of branching, it is generally from 0.05 to 2% by mole based onthe amount of the dihydric phenol in the aqueous phase.

In producing the polycarbonate resin, an organic phase for dissolvingthe yielded polymer therein is used. This organic phase should compriseany desired inert organic solvent in which, at the reaction temperatureand reaction pressure, phosgene and reaction products such as acarbonate oligomer and polycarbonate dissolve but water does notdissolve (in such a sense that the solvent does not give a solution withwater).

Typical inert organic solvents include aliphatic hydrocarbons such ashexane and n-heptane, chlorinated aliphatic hydrocarbons such asmethylene chloride, chloroform, carbon tetrachloride, dichloroethane,trichloroethane, tetrachloroethane, dichloropropane, and1,2-dichloroethylene, aromatic hydrocarbons such as benzene, toluene,and xylene, chlorinated aromatic hydrocarbons such as chlorobenzene,o-dichlorobenzene, and chlorotoluene, and substituted aromatichydrocarbons such as nitrobenzene and acetophenone. Preferably usedamong these are chlorinated hydrocarbons, e.g., methylene chloride orchlorobenzene.

These inert organic solvents can be used either alone or as a mixturewith one or more other solvents.

The production of the above-described polycarbonate resin can beconducted in such a preferred manner that a condensation catalyst is fedduring the contact of an aqueous phase with an organic phase prior tocontact with phosgene to thereby form an emulsion in the presence of thecondensation catalyst. It is a matter of course that a condensationcatalyst may be fed during contact with phosgene if desired. Any desiredcondensation catalyst can be selected from many condensation catalystsused in the interfacial polycondensation method. Especially preferred ofthese are trialkylamines, N-ethylpyrrolidone, N-ethylpiperidine,N-ethylmorpholine, N-isopropylpiperidine, and N-isopropylmorpholine. Inparticular, triethylamine and N-ethylpiperidine are suitable.

In the above process, there is no particular limitations on methods ofreaction with phosgene, and a technique advantageous for thermalstability can be employed. For example, use can be made of a method inwhich the phosgene to be used is purified before use by removing freechlorine, which is a low-boiling impurity, from the phosgene byadsorption in order to improve the purity of the starting materials tobe used, and a method in which methylene chloride (organic phase) and analkali metal salt of a dihydric phenol (aqueous phase) as other feedmaterials are emulsified beforehand and this emulsion having anincreased interfacial area is contacted with phosgene to thereby causethe reaction to proceed while keeping a growing monochloroformatepredominant.

In this case, the aqueous phase to be emulsified should comprise atleast three ingredients, i.e., water, a dihydric phenol, and an alkalimetal hydroxide. In the aqueous phase, the dihydric phenol reacts withthe alkali metal hydroxide, e.g., sodium hydroxide or potassiumhydroxide, to yield a water-soluble alkali metal salt. Although it is,of course, preferred to mix the above three ingredients to prepare ahomogeneous aqueous solution as an aqueous phase prior to contact withan organic phase, it is possible to mix part or all of these threeingredients during contact with an organic phase according to need. Themolar proportion of the dihydric phenol to the alkali in the aqueousphase is preferably from 1:1.8 to 1:3.5, more preferably from 1:2.0 to1:3.2. In preparing such an aqueous solution, the temperature thereof ispreferably regulated to 20° C. or higher, preferably from 30 to 40° C.However, since use of too high a temperature results in oxidation of thedihydric phenol, it is preferred to use a lowest necessary temperature.In addition, it is preferred to conduct the solution preparation in anitrogen atmosphere or to add a small amount of a reducing agent, e.g.,hydrosulfite.

The reaction temperature in obtaining an oligomer is 80° C. or lower,preferably 70° C. or lower, more preferably in the range of from 10 to65° C. If the reaction temperature is too high, side reactions cannot beinhibited, resulting in an impaired phosgene material unit. On the otherhand, too low reaction temperatures are undesirable in that therefrigeration load is increased to cause a cost increase, althoughpreferred from the standpoint of reaction control.

In the stage where an oligomer is obtained, the organic phase may haveany value of oligomer concentration as long as the oligomer obtained issoluble. Specifically, the oligomer concentration is about from 10 to40% by weight. The proportion of the organic phase to the aqueoussolution of an alkali metal hydroxide of the dihydric phenol, i.e., tothe aqueous phase, is preferably from 0.2 to 1.0 in terms of volumeratio. The oligomer obtained under such condensation conditions has anaverage molecular weight (Mv) of generally about from 500 to 10,000,preferably from 1,600 to 4,500. However, the average molecular weightthereof is not particularly limited.

The oligomer thus obtained is converted to a high-molecularpolycarbonate under polycondensation conditions in an ordinary manner.In a preferred embodiment, the organic phase containing the oligomerdissolved therein is separated from the aqueous phase and any of theaforementioned inert organic solvents is added thereto according to needto regulate the concentration of the oligomer. Specifically, the amountof the solvent is regulated so that the concentration in the organicphase of the polycarbonate to be obtained through polycondensation willbe generally from 5 to 30% by weight. Thereafter, an aqueous phasecomprising water and an alkali metal hydroxide is freshly added and thecondensation catalyst is preferably added in order to further regulatethe polycondensation conditions. The desired polycondensation is thencompleted by the interfacial polycondensation method. The proportion ofthe organic phase to the aqueous phase during the polycondensation ispreferably about from 1:0.2 to 1:1 in terms of the volume ratio of theorganic phase to the aqueous phase.

After completion of the polycondensation, the organic phase is washedwith an alkali such as NaOH until the residual chloroformate groups arediminished to, e.g., 0.1 μnmol/g or below. Thereafter, the organic phaseis washed until all the electrolytes are removed. Finally, the inertorganic solvent is removed from the organic phase in a suitable mannerto isolate the polycarbonate. The polycarbonate thus obtained generallyhas an average molecular weight (Mv) of about from 10,000 to 100,000.However, the Mv of the polycarbonate suitable for disk use is generallyfrom 13,000 to 20,000, preferably about from 14,000 to 18,000.

In the case where polycarbonates are formed into optical molded objects,a higher molding temperature should be selected according to the bitdistance and depth in the stamper to be used. However, as in the case ofthe above-described object resin of the present invention, for which aspecial substituted phenol, especially an alkylphenol, had to beselected, the molding temperature to be selected is generally about from340 to 400° C., preferably about from 350 to 390° C., more preferablyabout from 360 to 385° C., so as to cope with considerably increasedstorage capacities.

In this specification, the average molecular weight (Mv) of an oligomeror polycarbonate is a value calculated from the concentration (C)thereof (0.6 g/dl solution in methylene chloride) and the specificviscosity (ηsp) determined at a temperature of 20° C., using thefollowing two equations.

ηsp/C=[η](1.+0.28ηsp)

[η]=1.23×10⁻⁵×Mv^(0.83)

Various additives can be added in effective amounts to the polycarbonateresin obtained by the method described above, during the separationthereof from the reactor or before or during the processing thereof.Examples thereof include stabilizers, release agents, combustionretarders, antistatic agents, fillers, fibers, and impact strengthmodifiers.

These polycarbonate resins can be processes by injection molding,extrusion molding, or the like into various molded objects, e.g., films,fibers, and boards. Such objects are used in various technical fields,e.g., the electric part or building industry, and as materials forlighting appliances and materials for optical apparatuses, inparticular, the housings of illuminators, optical lenses, optical disks,and audio disks. The polycarbonate resins are advantageously usedespecially in the optical field for which high-temperature molding isnecessary.

Optical information recording media generally employ a polycarbonateresin as substrates. Known are optical disks for reproducing only (CD,CD-ROM, DVD-ROM, etc.), optical disks for recording and reproducing(write-once type: CD-R, DVD-R, etc.), and optical disks for recording,reproducing, erasing, and rewriting (rewritable type: MO, CD-RW,DVD-RAM, etc.).

EXAMPLES

The present invention will be explained below in detail by reference toExamples, but the invention should not be construed as being limitedthereby unless the invention departs from the spirit thereof.

Symbols or abbreviations having the following meanings or used in theExamples.

Symbols or abbreviations Meaning BPA Bisphenol A BPA-Na Sodium salt ofbisphenol A GPC Gel permeation of chromatography

Examples 1 to 8

An aqueous phase prepared by dissolving 16.31 kg/hr bisphenol A, 5.93kg/hr NaOH, and 101.1kg/hr water in the presence of 0.018 kg/hrhydrosulfite at 35° C. and cooling the solution to 25° C. and an organicphase consisting of 68.0 kg/hr methylene chloride cooled to 5° C. werefed to a stainless-steel piping having an inner diameter of 6 mm and anouter diameter of 8 mm to mix the two phases within the piping. Thismixture was emulsified with a homomixer (trade name, T.K Homomic LineFlow Type LF-500; manufactured by Tokushu Kika Kogyo Co., Ltd.) toprepare an emulsion.

The thus-obtained emulsion consisting of an aqueous BPA-Na solution(aqueous phase) and methylene chloride (organic phase) was taken out ofthe homomixer through a piping having an inner diameter of 6 mm and anouter diameter of 8 mm and extending from the homomixer. This emulsionwas introduced into a pipe reactor made of Teflon which had an innerdiameter of 6 mm and a length of 34 m and had been connected to thepiping, and was then contacted therein with 7.5 kg/hr liquefied phosgeneseparately introduced thereinto through a pipe cooled to 0° C. Thisliquefied phosgene used was one which had been treated by packing acylindrical vessel having a diameter of 55 mm and a height of 500 mmwith activated carbon (trade name, Yashicoal S; manufactured by TaiheiChemical Industrial Co., Ltd.; properties are shown below) and passingthe phosgene through the vessel at −5° C., 7.2 kg/hr, and an SV of 3.

Activated carbon used: Particle size: 30-60 mesh True density: 2.1 g/ccPorosity: 40% Specific surface area: 1,200 m²/g Pore volume: 0.86 cc/g

The feed materials were passed together with the phosgene through thepipe reactor at a linear velocity of 1.7 m/sec over a period of 20seconds, during which phosgene reaction and oligomerization reactionwere conducted. In this stage, the reaction temperature was regulated to60° C. in each reaction and the reaction mixture was externally cooledto 35° C. before being introduced into the subsequent oligomerizationvessel.

The emulsion obtained from the pipe reactor, which had undergoneoligomerization, was introduced into a reaction vessel having a capacityof 50 liters and equipped with a stirrer. The emulsion was then stirredin an N₂ atmosphere at 30° C. to conduct oligomerization, whereby theunreacted BPA-Na present in the aqueous phase was completely consumed.Thereafter, the aqueous phase and organic phase were separated from eachother by standing to obtain a methylene chloride solution of anoligomer. For the oligomerization, triethylamine as a catalyst wasintroduced into the oligomerization vessel in an amount of 0.005 kg/hr,and the alkylphenol whose kind and amount (mol % (based on the dihydricphenol)) are shown in Table 1 and Table 2 was further introducedthereinto as a chain terminator. The ortho isomer content (ppm) of thealkylphenol is also shown in Table 1 and Table 2.

The dodecylphenol used in Examples 3 to 8 was produced in the followingmanner.

Feedstock dodecene heated to 50° C. was mixed with phenol heatedlikewise (4 mol per mol of the dodecene). This liquid mixture was passedthrough a column of an acid ion-exchange resin to conduct alkylationreaction. Since this alkylation was accompanied by heat generation, theliquid mixture was passed while removing heat therefrom in an amountcorresponding to the heat generation. The reaction mixture thus obtainedwas fed to a reaction column likewise packed with an acid ion-exchangeresin to isomerize the reaction product for converting the ortho isomerto the para isomer.

The dodecylphenol thus obtained was treated with a distillation columnfor initial phenol separation to remove the phenol, and then withanother column to remove heavy ends, e.g., the dialkylated phenol, asimpurities. Thus, a dodecylphenol product was obtained.

The alkylphenols used in the Examples each was one for which the orthoisomer being yielded was diminished by prolonging the ordinary periodsof the alkylation reaction and the isomerization reaction to two timesor more, and optionally strengthening the distilling condition.

A 23 kg portion of the above oligomer solution in methylene chloride wasintroduced into a reaction vessel having a capacity of 70 liters andequipped with a Pfaudler blade. Thereto was added 10 kg of methylenechloride for dilution, followed by 2.2 kg of 25 wt % aqueous NaOHsolution, 6 kg of water, and 2.2 g of triethylamine. The resultantmixture was stirred at 30° C. in an N₂ atmosphere to conductpolycondensation reaction for 60 minutes. Thus, a reaction mixturecontaining a polycarbonate was obtained.

To this reaction mixture were added 30 kg of methylene chloride and 7 kgof water. After the resultant mixture was stirred for 20 minutes, thestirring was stopped to separate the organic phase from the aqueousphase. To the separated organic phase was added 20 kg of 0.1 Nhydrochloric acid. This mixture was stirred for 15 minutes to extractthe triethylamine and the alkali ingredient remaining in a small amount.Thereafter, the stirring was stopped to separate the organic phase fromthe aqueous phase. Furthermore, 20 kg of pure water was added to theseparated organic phase and this mixture was stirred for 15 minutes,before the stirring was stopped to separate the organic phase from theaqueous phase. This operation was repeated (three times in total) untilchlorine ions came not to be detected in the extractant water.

The thus-obtained purified polycarbonate solution was granulated with akneader and dried to obtain a granular powder (flakes).

These flakes were kneaded with a 30-mm twin-screw extruder (manufacturedby Ikegai Corp.) at a resin temperature of 290° C. in an N₂ atmosphereand then pelletized (15 kg/hr). This treatment was conducted whiletaking sufficient care to avoid operational impurity inclusion(impurities derived from the hands and sweat of workers and from coolingwater).

The flakes obtained in each Example were examined for average molecularweight and molecular weight distribution. Furthermore, the pellets wereexamined for color tone. The results obtained are shown in Table 1 andTable 2. Further, “−” in the tables means “unmeasurement”.

The polycarbonate properties shown in the table were evaluated in thefollowing manners.

<1> Molecular Weight Distribution (Mw/Mn):

Using a GPC apparatus (trade name, HLC-8020; manufactured by TosohCorp.) and tetrahydrofuran (THF) as an eluent, each polycarbonate wasfractionated with four columns respectively packed with four packingsfor high-performance GPC (trade name, TSK 500OHLX, 4000HLX, 300OHLX, and2000HLX; manufactured by Tosoh Corp). Detection was conducted based on adifference in refractive index. From the chart thus obtained, theweight-average molecular weight (Mw) and the number-average molecularweight (Mn) were determined in terms of standard polystyrene. The valueof Mw/Mn was calculated therefrom.

<2> Color Tone (YI):

<Molding of Sample Plate>

The pellets obtained in the above-described manner were plasticated withan injection molding machine (trade name, JSW J75EII; manufactured bythe Japan Steel Works, Ltd.) at 360° C., subsequently allowed to residein the cylinder for 180 seconds, and then molded into 60 mm-squaresample plates each having a thickness of 3.2 mm.

<Determination of Color Tone>

The sample plates obtained respectively by the first and tenth shots inthe above molding mere examined for color tone (YI (yellowness index))with a color difference meter (trade name, CM-3700D; manufactured byMinolta Co., Ltd.), and the difference therebetween (ΔYI) wasdetermined. Smaller found values of YI for the first shot indicate thatmolded objects having a satisfactory color tone are obtained insteady-state molding, while smaller differences in YI (ΔYI) between thefirst and the tenth shots indicate that the molding material hassatisfactory high-temperature thermal stability.

<3> Long-term Reliability Test:

Using an injection molding machine (trade name: CD Mini) manufactured bySumitomo Heavy Industries, Ltd., CD substrates having a diameter of 80mm and a thickness of 1.26 mm were molded.

Cylinder temperature: 300° C. Mold temperature: 80° C./70° C. Cycletime: 10 seconds

Molding was stably conducted over 100 shots. Of the thus-molded CDsubstrates, ten substrates regarded as stable products were taken out.These ten substrates were held in an atmosphere having a temperature of85° C. and a humidity of 85% RH for 2 days.

Thereafter, the whole surface of each substrate was closely examinedwith a polarizing microscope for hydrolytically generated white spots.The long-term reliability is expressed in terms of the number of suchwhite spots per ten substrates.

<4> Melt Viscosity:

A capillograph (trade name, Capillograph 1B; manufactured by Toyo SeikiSeisaku-Sho, Ltd.) was used as a means for comparing melt flowability.The melt viscosity was measured under the conditions of L (orificelength)/D (orifice diameter)/B (barrel diameter)=40/1/9.55 (mm), 250°C., and a shear rate γ of 100 (sec⁻¹).

<5> Total Light Transmittance (ASTM D1003):

The 3.2 mm-thick sample plate described above was examined for totallight transmittance as a measure of transparency, which is required ofdisk substrates. Smaller values of total light transmittance indicatethat the samples are insufficient in the transparency originallypossessed by polycarbonates; such samples can be judged to be unsuitablefor use as optical materials.

<6> Comparison in Transferability from Stamper in Disk Molding andEvaluation of Substrate Properties:

Using molding machine SD30, manufactured by Sumitomo Heavy Industries,Ltd., a substrate having a diameter of 120 mm and a thickness in therecording region of 0.6 mm was molded under the following conditions.The stamper used was one conforming to 4.7 GB DVD-R.

This stamper had a track pitch of 0.74 μm and a groove depth of 170 nm.

Cylinder temperature: 385° C. Mold temperature: 130° C./124° C. Chargingtime: 0.09 sec Cooling time: 9.0 sec Compression force (ton): 20-12-8-5

After the polycarbonate substrate was molded under these conditions, thedepth of the grooves transferred thereto was measured with respect tothe outermost groove in the recording it region. Thus, transferabilitywas compared.

<Birefringence>

The maximum and the minimum values of in-plane birefringence weremeasured with automatic birefringence analyzer ADR-130N, manufactured byOak Seisaku-sho.

<Mechanical Property>

The mechanical properties of the substrate were evaluated according tospecifications for DVD-R (DVD Specifications for Recordable Disc/Part. 1Physical Specifications Ver. 1.0 July 1997).

The samples which satisfied the specifications with a sufficient marginare indicated by ◯, while those which barely satisfied thespecifications are indicated by Δ.

Comparative Examples 1 to 4

The same procedure as in Example 1 was conducted, except that thealkylphenols shown in Table 1 were used as chain terminators. All thealkylphenols used had been treated in the ordinary reaction time andordinary isomerization time; most of the commercial products generallyavailable have the same compositions as those. The results obtained areshown in Table 1.

Comparative Example 5

The same procedure as in Comparative Example 1 was conducted, exceptthat the cylinder temperature and the mold temperature during moldingwere changed to 395° C. and 132° C./126° C., respectively. The resultsobtained are shown in Table 1.

TABLE 1 Comparative Example 1 Example 2 Example 3 Example 4 Example 5Example 1 Kind of alkylphenol t-octylphenol t-octylphenol dodecylphenoldodecylphenol dodecylphenol t-butylphenol Addition amount (mol % basedon dihydric phenol) 6.1 3.9 6.3 4.0 6.3 5.9 Ortho isomer content (ppm)1,100 960 19,200 15,600 15,300 60 Calculated value of right side ofrelationship (i) 1,905 1,905 33,113 33,113 33,113 110 Average molecularweight of yielded polymer (Mv) 15,200 21,100 15,300 21,500 15,100 15,600Molecular weight distribution (Mw/Mn) 2.67 2.78 2.72 2.80 2.62 2.68 YI:1st shot (360° C.; cycle time, 180 sec) 2.0 1.6 1.95 1.72 1.65 1.35 YI:10^(th) shot (360° C.; cycle time, 180 sec) 2.5 1.95 2.40 2.06 2.03 1.68ΔYI 0.5 0.35 0.45 0.34 0.38 0.33 Long-term reliability test (number ofwhite spots — — — — — 0 per 10 substrates) Melt viscosity (250° C. atγ =100 sec⁻¹) 11,000 — 9,000 — 9,000 12,000 Total light transmittance 91 9191 91 91 92 Substrate Depth of transferred groove (nm) 160 — 170 — 170100 Properties In-plane birefringence (× 10⁻⁶) −9 to 29 — −13 to 20 —−10 to 15 −11 to 29 Min-Max Mechanical property ◯ — ◯ — ◯ ◯ ComparativeComparative Comparative Comparative Example 2 Example 3 Example 4Example 5 Kind of alkylphenol t-octylphenol dodecylphenol nonylphenolt-butylphenol Addition amount (mol % based on dihydric phenol) 6.1 6.36.2 5.9 Ortho isomer content (ppm) 2,200 35,800 5,600 60 Calculatedvalue of right side of relationship (i) 1,905 33,113 3,890 110 Averagemolecular weight of yielded polymer (Mv) 15,400 15,800 15,200 15,400Molecular weight distribution (Mw/Mn) 2.68 2.70 2.68 2.69 YI: 1st shot(360° C.; cycle time, 180 sec) 3.2 4.6 5.5 1.32 YI: 10^(th) shot (360°C.; cycle time, 180 sec) 4.1 5.8 6.8 1.68 ΔYI 0.9 1.2 1.3 0.36 Long-termreliability test (number of white spots — 1.8 1.5 0 per 10 substrates)Melt viscosity (250° C. atγ = 100 sec⁻¹) 9,500 9,200 9,000 12,000 Totallight transmittance 89 88 88 92 Substrate Depth of transferred groove(nm) 160 170 170 160 Properties In-plane birefringence (× 10⁻⁶) −12 to26 −10 to 25 −15 to 22 −15 to 16 Min-Max Mechanical property ◯ ◯ ◯ — *Substrate properties: with respect to transfer, numerals close to 170 nmare satisfactory; with respect to birefringence, smaller values ofMin-Max difference are satisfactory. * In Comparative Example 1 in thetable, since the alkyl substituent of the phenol had a small number ofcarbon atoms, the polymer had poor melt flowability and was inferior intransferability as shown under Substrate Properties. * Substrateproperties: with respect to transfer, numerals close to 170 nm aresatisfactory; with respect to birefringence, smaller values of Min-Maxdifference are satisfactory. * In Comparative Examples 2 to 4, since thealkylphenols had high ortho isomer contents, the substrates had a verypoor hue and were unsuitable for use as substrates, although flowabilityand transferability were satisfactory. * In Comparative Example 5, thesubstrate had poor mechanical properties because the alkylphenol usedhad a small number of carbon atoms and molding was conducted underseverer conditions. * Substrate properties: with respect to transfer,numerals close to 170 nm are satisfactory; with respect tobirefringence, smaller values of Min-Max difference are satisfactory.

TABLE 2 Example 6 Example 7 Example 8 Kind of alkylphenol dodecyl-dodecyl- dodecyl- phenol phenol phenol Addition amount 6.3 4.0 6.3 (mol% based on dihydric phenol) Ortho isomer content (ppm) 9,200 9,900 8,500Calculated value of right side 33,113 33,113 33,113 of relationship (i)Average molecular weight of 15,300 21,500 15,100 yielded polymer (Mv)Molecular weight distribution 2.52 2.65 2.57 (Mw/Mn) YI: 1st shot 1.951.80 1.65 (360° C.; cycle time, 180 sec) YI: 10th shot 2.20 2.10 2.03(360° C.; cycle time, 180 sec) ΔYI 0.25 0.30 0.38 Long-term reliabilitytest 0.1 0 0.1 (number of white spots per 10 substrates) Melt viscosity9,000 — 9,000 (250° C. at {dot over (γ)} = 100 sec⁻¹) Total lighttransmittance 91 91 91 Substrate Properties Depth of 170 — 170transferred groove (nm) In-plane −10 to 15 — −10 to 15 birefringence (×10⁻⁶): Min-Max Mechanical ◯ — ◯ property

POSSIBILITY OF INDUSTRIAL APPLICATION

The polycarbonate resin of the present invention has an averagemolecular weight of generally from 10,000 to 100,000. It not only givesmolded objects having excellent properties inherent in polycarbonateresins, but has an advantage that given molded articles are obtainedtherefrom at lower molding temperatures because it shows significantlyimproved flowability during molding. In addition, less colored moldedobjects can be obtained therefrom. Consequently, the polycarbonate resinhas an advantage of being usable in a far wider range of applicationsthan conventional polycarbonate resins. Furthermore, since thepolycarbonate resin has an advantage of being excellent intransferability from molds or stampers even at low molding temperatures,it is possible to obtain less deteriorated products in a high yield.

What is claimed is:
 1. A polycarbonate resin obtained by reactingstarting materials comprising a dihydric phenol, a carbonate material,and a chain terminator comprising a p-substituted phenol (hereinafterreferred to as a para isomer) represented by the following generalformula (I), characterized in that the amount of an o-substituted phenol(hereinafter referred to as an ortho isomer) contained as an impurity inthe chain terminator used satisfies the following relationship (i):

(wherein R is an organic group having 6 to 30 carbon atoms)$\begin{matrix}{{\frac{\left( {{ortho}\quad {isomer}\quad {amount}} \right)}{\left( {{para}\quad {isomer}\quad {amount}} \right) + \left( {{ortho}\quad {isomer}\quad {amount}} \right)} \times 10^{6}} \leq 10^{({{0.31 \times {({{number}\quad {of}\quad {C'}s})}} + 0.8})}} & (i)\end{matrix}$

(wherein “number of C's” represents the number of carbon atoms in thesubstituent organic group of the substituted phenols).
 2. Thepolycarbonate resin of claim 1, which when molded at 360° C. and a cycletime of 180 seconds gives molded objects (3.2 mm thick) having a YI of2.5 or lower and a difference in YI between the first shot and the tenthshot (hereinafter referred to as ^(Δ)YI) of 0.8 or smaller.
 3. Apolycarbonate resin obtained by reacting starting materials comprising adihydric phenol, a carbonate material, and a chain terminator comprisinga p-substituted phenol represented by the following general formula (I),said polycarbonate resin, when molded at 360° C. and a cycle time of 180seconds, giving molded objects (3.2 mm thick) having a YI of 2.5 orlower and a difference in YI between the first shot and the tenth shot(hereinafter referred to as ΔYI) of 0.8 or smaller:

(wherein R is an organic group having 6 to 30 carbon atoms).
 4. Thepolycarbonate resin of claim 2, wherein the YI is 1.8 or lower and theΔYI is 0.5 or smaller.
 5. The polycarbonate resin of claim 1, whereinthe p-substituted phenol as the chain terminator is a p-alkylphenolrepresented by the following general formula (II):

(wherein R′ is an alkyl group having 6 to 30 carbon atoms).
 6. Asubstrate for optical information recording media which comprises thepolycarbonate resin of claim
 1. 7. An optical information recordingmedium comprising a substrate comprising the polycarbonate resin ofclaim 1 and an optical information recording layer formed on thesubstrate.
 8. A polycarbonate resin obtained by reacting startingmaterials comprising a dihydric phenol, a carbonate material, and achain terminator comprising a p-substituted phenol (hereinafter referredto as a para isomer) represented by the following general formula (III),wherein the amount of an o-substituted phenol (hereafter referred to asan ortho isomer) contained as an impurity in the chain terminator usedsatisfies the following relationship (iv):

(wherein R is an organic group having 11 to 15 carbon atoms)$\begin{matrix}{{\frac{\text{(ortho isomer amount)}}{\text{(para isomer amount)} + \text{(ortho isomer amount)}} \times 10^{6}} < {10,000.}} & ({iv})\end{matrix}$


9. The polycarbonate resin of claim 8, which when molded at 300° C. anda cycle time of 10 seconds gives molded CD products (1.26 mm thick) inwhich the number of hydrolytically generated white spots appearing onthe substrate surface when the CD products are held in an atmospherehaving a temperature of 85° C. and a humidity of 85% RH for 2 days is 5or smaller per ten CD's.
 10. A polycarbonate resin obtained by reactingstarting materials comprising a dihydric phenol, a carbonate material,and a chain terminator comprising a p-substituted phenol represented bythe following general formula (III), said polycarbonate resin, whenmolded at 360° C. and a cycle time of 180 seconds, giving molded objects(3.2 mm thick) having a YI of 2.5 or lower and a difference in YIbetween the first shot and the tenth shot (hereinafter referred to asΔYI) of 0.8 or smaller:

(wherein R is an organic group having 11 to 15 carbon atoms).
 11. Thepolycarbonate resin of claim 8, wherein the p-substituted phenol as thechain terminator is a p-alkylphenol represented by the following generalformula (IV):

(wherein R′ is an alkyl group having 11 to 15 carbon atoms).
 12. Asubstrate for optical information recording media which comprises thepolycarbonate resin of claim
 8. 13. An optical information recordingmedium comprising a substrate comprising the polycarbonate resin ofclaim 8 and an optical information recording layer formed on thesubstrate.
 14. The polycazbonate resin of claim 3, wherein the YI is 1.8or lower and the ΔYI is 0.5 or less.
 15. The polycarbonate resin ofclaim 10, wherein the p-substituted phenol as the chain terminator is ap-alkylphenol represented by formula (IV):

wherein R′ is an alkyl group having 11 to 15 carbon atoms.